This invention relates to a method of diagnosing the condition of a steering system of a vehicle during use and to a diagnostic system suitable for fitment to a vehicle that carries out the method. It also relates to an electric power steering system which is able to compensate for certain changes in its condition.
The correct operation of the steering system of a vehicle is critical to its safety. In use, the system can become damaged or worn. For example, a component could be bent if struck by a rock that is flicked up from the road by the wheels of the vehicle. The bearings at the joints in the system or rack gear could become worn or damaged. Wear or damage can make the car unsafe to drive, or at the least cause the steering to feel strange. Worn bearings can make the steering wheel harder to turn by increasing the friction that must be overcome at the joint. If wear or damage is severe, it is probable that a driver would notice and take the vehicle to a garage for repair. Less severe damage, still potentially a safety concern, is unlikely to be noticed by the driver. This is especially true for electric power assisted steering, in which torque is applied to the column by a motor acting through a worm and wheel. Wear in the rack may be undetectable by the driver, but could lead to premature failure of the assistance system. Normal servicing for vehicles often calls for little more than a visual inspection of the steering at regular intervals, which may not pick up wear or damage.